1. Field of the Invention
The invention is related to a camera flash photographing control device, in which digital or analogue information for photographing obtained on the camera side are once digital-processed, and information for controlling a shutter is obtained by analogue means to control the degree of flash light emission.
2. Description of the Prior Art
Generally, when camera flash light photographing is automatic, conditions for photographing are set by a camera iris mechanism, information to be obtained at the time of light measurement of an object or information required for exposure of film, shutter and an iris, as well as the degree of flash light emission are controlled on the basis of these set conditions for photographing. In this case, information obtained from the brightness of an object and sensitivity of film are detected as a level of an analogue signal converted to a voltage level at a resistor or a capacitor in many cases. For final control of the degree of flash light emission, means in which discharge charge corresponding to the degree of light emission thereof is integrated are used in many cases. Therefore, the degree of flash light emission is usually analogue-processed. Thus, no inconvenience occurs if all these pieces of information can be analogue-processed simply and precisely when information to be input is a level of analogue.
However, there are various bits of information for determining conditions for photographing, and these have complicated mutual relationships in many cases. Therefore, it is difficult to analogue-process all information without sacrificing the operability of a camera device. This explains why analogue processing means have more complicated circuitry than that by digital processing means. Thus, it is recommended to process once after converting information to digital signal, even when information is input as a level of analogue signal. Most camera devices these days incorporate a digital processing circuit.
Sometimes, it is more convenient to directly detect, for instance, sensitivity information of a film along with information for setting conditions for photographing as digital information using a gray code plate, etc. In this case, information to be input includes information on the sensitivity of film as a digital signal, and luminance information of an object and iris information of a photographing lens, etc. both of which are analog signals and are obtained at the time of light measurement. Thus, at least two analogue-digital (A-D) converters are required to process this latter information. Information on the sensitivity of film to be input as a level of a digital signal is input into the digital-analogue (D-A) converter after being processed in an arithmetic circuit into which information on luminance and iris output from each A-D converter are input. In the prior art, the degree of flash light emission is controlled by comparing output corresponding to this D-A converted information on film sensitivity with output of an integrator which integrates according to the degree of flash light emission in analogue. Thus, traditional devices required at least two A-D converters and one D-A to control the degree of flash light emission.
However, requirement of several converters is not satisfactory for a camera device for which simplification of circuitry is desired. Therefore, means for integrating each converter to perform D-A and A-D conversions simultaneously have been demanded.